Hi,
First, your database server is not running so you cannot do anything.
So, I thoink you need to follow the steps :
1 - initdb -D /Thedirectory where are your data (With RPM maybe you don't need this step)
2 - postmaster -S -D /Thedirectory -i & (maybe have you a /etc/init.d/postgres*, in this case you only need to tape /etc/init.d/postgres* start, I put postgres* because I don't know exactky the name)
And now you can create an user and a database
Bruno